In the field of processing apparatuses which use a plasma, such as dry etching apparatuses, ashing apparatuses and plasma CVD apparatuses, used in the manufacturing process of semiconductor devices and liquid crystal displays, plasma sources of the apparatuses are required to provide large-diameter design in association with the recent upsizing of substrates to be treated. Furthermore, on the other hand, high-density design of a plasma in a high vacuum is required in order to ensure etching rate, film forming rate and throughput.
For the high-density design of a plasma among these requirements, a method by which an inductively coupled plasma (hereinafter referred to as an ICP) is generated by use of a high-frequency wave is adopted in order to promote plasma excitation efficiency. An IPC is such that a high-frequency current is caused to flow mainly through an antenna excitation coil and an induction field is generated in a vacuum, with the result that a high-density plasma can be uniformly formed in a high vacuum.
An example of a conventional plasma processing apparatus which uses an ICP is shown in FIG. 14. In FIG. 14, the numeral 21 denotes a vacuum container (process chamber) which performs substrate etching processing etc., the numeral 22 an insulating partition of quartz etc. provided in part of the vacuum container, the numeral 23 a high-frequency antenna of a go-around shape which is provided in loop or spiral shape along the wall surface of the insulator wall 22 on the atmosphere side with one or more turns, the numeral 24 a high-frequency power source which supplies high-frequency power to the high-frequency antenna, the numeral 25 an exhaust opening, the numeral 26 a discharge chamber in which a discharge plasma is generated, and the numeral 27 a substrate electrode.
In the conventional method shown in FIG. 14, it is necessary to increase the wall thickness of the insulating partition 22 to a thickness which is as large as 10 to 30 mm in order to obtain mechanical strength necessary for resisting a pressure difference between the outside air under atmospheric pressure and the interior of the discharge chamber 26 in a high vacuum when the diameter of the discharge pressure is to be increased to not less than 400 mmφ. For this reason, the intensity of the induction field radiated from the high-frequency antenna 23 decreases exponentially with increasing distance from the antenna and the discharge efficiency worsens, with the result that the inductance of the antenna 23 increases, posing problems such as an increase in the high-frequency voltage occurring in the antenna.
On the other hand, instead of providing an antenna so as to go around like this on the side surface of the discharge chamber, there was available a method by which the top surface of the discharge chamber of the vacuum container is used as the top plate of the insulator and an antenna is provided outside the top plate. This method posed the problem that the required thickness of the insulator of the top plate is as large as 30 to 50 mm in order to ensure mechanical strength when the diameter of the discharge chamber is to be increased to not less than 400 mmφ, whereas the thickness of the insulator of the top plate is about 20 mm when the present discharge chamber diameter is 300 mmφ.
In the conventional inductively coupled plasma generator in which a high-frequency antenna is provided on the insulating partition of the vacuum container or on the wall surface on the top plate on the outside air side, the thickness of the insulator has to be substantially increased with increasing diameter of the discharge chamber. Besides, the conventional inductively coupled plasma generator posed the problem that the utilization efficiency of the high-frequency power which is input is low because only the induction field component radiated to the side of a face in contact with the insulating partition of the vacuum container or the top plate out of the entire induction field radiated from the antenna is utilized in maintaining the discharge.
The object of the present invention is to provide a plasma generator which generates, in a stable manner, a large-diameter, large-volume, high-density plasma which is not limited by the shape, diameter and length of a discharge chamber.